Hydrocarbon recovery

ABSTRACT

Low concentrations, 1-10% of potassium salt, especially potassium formate, are used in a drilling fluid in oil production. Preferably they are used with guar derivatives, most preferably carboxymethyl hydroxypropyl guar. The concentration of potassium formate is maintained at the desired level by adjusting the potassium formate to maintain a desired Zeta potential in the circulating drilling fluid. The potassium formate/guar derivative composition may be used in the substantial absence of hydrophilic clay additive.

TECHNICAL FIELD

[0001] In the recovery of hydrocarbons from the earth, a lowconcentration of potassium formate is used in aqueous drilling fluid,preferably with a viscosifying amount of polygalactomannan theconcentration of potassium formate being controlled as a function ofZeta potential of the drilling fluid.

BACKGROUND OF THE INVENTION

[0002] Potassium salts have been used to help to control the intrusionof shale and clay into fluids produced from subterranean formations. Thepresence of potassium in brines which come in contact with shale andclay in underground formations will inhibit the absorption of sodiuminto the brine from the clay or shale, thus reducing permeabilitydamage. However, it has been difficult to determine and control theoptimum amounts of potassium to use.

[0003] The use of potassium formate in formation treatment fluidscontaining cationic formation control additives is disclosed by Kevin W.Smith in U.S. patent application Ser. No. 09/812,422. Filed Mar. 20,2001. In U.S. patent application Ser. No. 09/803,501 filed Mar. 9, 2001,Kevin W. Smith discloses the use of potassium formate together with guarfor reducing permeability damage by formation treatment fluids.

[0004] The capillary suction test is known as a method widely used todetermine the tendency of clay and shale to adsorb potassium ion.Performance of a brine in the capillary suction test (CST) is used as aguide to the quantity of potassium deemed to be necessary to stabilizethe formation, particularly to inhibit sloughing of shale and swellingof clay. Lauzon, in U.S. Pat. No. 4,507,210, teaches the use of thecapillary suction test and/or Zeta potential to adjust or formulate aclay and shale treatment medium which may include a hydroxypropyl guargum (column 5, lines 58-59), for minimizing swelling and dispersion ofsubterranean formation particles. Zeta Potential is the potential at theshear interface created by a colloidal or other particle moving througha liquid medium with its associated ions, in an electric field. Zetapotential has been used as part of a method to extend bit life—see thereview of the art in Engelman et al U.S. Pat. No. 5,196,401, col. 2lines 22-36; see also their FIG. 2. Zeta potential has been used tostudy clay control in the presence of polymers, in uranium mining—seeHjelmstad's U.S. Pat. No. 4,925,247.

[0005] In U.S. Pat. No. 5,489,674 to Yeh and U.S. Pat. No. 5,536,825 toYeh et al, the authors discuss guar gum as a natural polygalactomannan.They go on to describe various derivatives of guar, includingcarboxymethyl hydroxypropyl guar—see column 5, line 49 of U.S. Pat. No.5,489,674 and line 51, column 5 of U.S. Pat. No. 5,536,825. At line 23of column 3 of Dobson et al U.S. Pat. No. 5,629,271,carboxymethylhydroxypropyl guar is mentioned as a possible viscosifierand suspending agent in a “clay-free” formation treatment fluid which,however, includes an “ultra fine filtrate reducing agent.”

[0006] The full benefits of the varied elements of the prior artdiscussed above have yet to be realized in the well drilling and relatedarts.

SUMMARY OF THE INVENTION

[0007] We have determined that the prior art has generally overestimatedthe amount of potassium necessary to stabilize clay and shale during thehydrocarbon recovery process. Potassium formate is particularlyeffective in low concentrations. Further, the small amounts of potassiumformate able to stabilize the clay and shale can be maintained byreplenishing it as a function of the Zeta Potential of the drillingfluid.

[0008] Our invention provides that an optimum concentration of potassiumsalt can he maintained in a drilling or formation treatment fluid bymonitoring the Zeta Potential of the drilling or formation treatmentfluid and adjusting the potassium salt concentration as a functionthereof We prefer to use potassium formate in the drilling or formationtreatment fluid, but our invention is applicable to the use of anypotassium salt in a drilling or formation treatment fluid. Accordingly,our invention includes the intermittent measurement of Zeta potential,so that the potassium content of the circulating drilling fluid can beadjusted according to the results as the potassium formate is consumedor its concentration varies with other conditions, such as at differentdepths of the application of the fluid—that is, in different strata.

[0009] We have found that, when low concentrations of potassium formateare used together with a polygalactomannan (including derivatives suchas the guar derivative carboxymethylhydroxypropyl guar), it is notnecessary to include a bentonitic clay or other solid hydrophilicmaterial with a drilling fluid. Our invention includes the use of lowconcentrations (1-10%, preferably 2-6% by weight) of potassium formatein drilling and formation treatment fluids, as the only significantsource of potassium ions, in the substantial absence of an added solidhydrophilic clay. By a solid hydrophilic clay, we mean bentonite,attapulgite, sepialite, or any other hydrophilic clay which mightconventionally be added to the drilling fluid.

[0010] Preferably, our invention includes the use of a combination of alow concentration (1-10% by weight) of potassium formate and aviscosifying amount of carboxymethyl hydroxypropyl guar. We may use thehydroxymethylhydroxypropyl guars described in the above identified Yehpatents, which are hereby incorporated by reference in their entirety.

DETAILED DESCRIPTION OF THE INVENTION

[0011] A typical drilling formulation within our invention comprises anaqueous solution of (a) 1% to 10%, preferably 2% to 6%, by weightpotassium formate and (b) 0.0 1% to 1.2% of a polygalactomannan orderivative thereof, preferably 0.1% to 1% by weight. Preferably thepolygalactomannan is carboxymethyl hydroxypropyl guar. The percentagesare by weight based on the completed drilling fluid. We also may includecalcium carbonate in an amount desired to help control circulation lossor to increase the density of the drilling fluid, i.e. up to 50% byvolume of the drilling fluid. With this composition, with or without thecalcium carbonate, it is frequently not necessary to use a bentoniticclay or other hydrophilic clay to form a mud. Thus our inventionincludes a method of treating a hydrocarbon producing formation tostabilize shale and clay therein comprising contacting the hydrocarbonproducing formation with an aqueous formation treatment fluid comprising1% to 10% by weight of potassium formate and 0.01% to 1.2% of a guarderivative, in the substantial absence of a hydrophilic clay drillingadditive, and recirculating the aqueous formation treatment fluid in theformation. In order to maintain the potassium formate concentration inthe formation treatment fluid, the Zeta potential may be determined onsamples of circulating drilling fluid containing particles of shale orclay encountered in the well; the potassium formate concentration in thefluid is adjusted within the range of 1% to 10% to maintain a desiredZeta potential having an absolute value greater than 15 and correlatedto the desired potassium formate concentration.

[0012] The use and measurement of Zeta potential is well known, but itshould be understood that the above stated values of Zeta potential arein terms of millivolts. Millivolts are a commonly used unit for theexpression of Zeta potential as determined in a Zeta-Meter. The Zetapotential is a measure of the difference in static charge between (1) aparticle and any associated modifying substances or ions and (2) theliquid in which it is suspended. Readings are taken while the particlesand the suspending medium arc subjected to a DC current, and the readoutis a function of the velocity of the suspended particle, taking intoaccount the viscosity and other factors. When we use the term Zetapotential herein, we mean to include the electrophoretic mobility fromwhich the Zeta potential is derived, as well as any other expressionwhich is a direct function of Zeta potential. By a “Zeta potentialhaving an absolute value greater than 15” we that the Zeta potential inmillivolts, as a function of electrophoretic mobility of the shale andclay particles in the measurement sample) is either greater than +15 orlower than −15.

[0013] Tables 1 and 2 show that there is little or no correlationbetween capillary suction time (CST) and Zeta Potential where thepotassium salt used is potassium sulfate, but a correlation is evidentfor potassium formate.

[0014] In Tables 1 and 2, both the CST and Zeta potential were measuredin suspensions of Jean Marie shale at varying concentrations ofpotassium sulfate for Table 1 and potassium formate for Table 2. TABLE 1Potassium sulfate; 2% Jean Marie Shale % K₂SO₄ CST, seconds Zeta P 0 103−34 mv 0.1 70 −44 mv 0.5 56.1 −37 mv 1 40 −38 mv 5 23 −44 mv 10 21 −44mv

[0015] TABLE 2 Potassium Formate; 2% Jean Marie Shale % KCOOH CST,Seconds Zeta P 0 68 −35 mv 0.1 35.4 −33.5 mv 0.3 21.1 −33 mv 2.3 18.7−23 mv 4.8 16.9 −29 mv 9 19.5 −25

[0016] Table 3 also shows a correlation between CST and potassiumformate concentration. TABLE 3 Potassium Formate; 2% Black Stone Shale %KCOOH CST, Seconds Zeta P 0 155.3 −60 mv 0.1 103.7 −30 mv 0.3 57.8 −27.2mv 2.3 28 −24.6 mv 4.8 21.9 −25 mv 9 22.8 −28 mv

[0017] Tables 4 and 5 demonstrate the correlations of CST to Zetapotential for low concentrations of potassium formate in solutions ofvarying viscosity. Viscosity was imparted by varying concentrations of arandom copolymer of 20% acrylic acid and 80% diallyl dimethyl ammoniumchloride, designated as “Polymer”. TABLE 4 Potassium Formate; Jean MarieShale % KCOOH % Polymer CST, seconds Zeta Potential 0 0 59 −40 mv 0.16 035.7 −19 mv 0.16 0.03 12.1 −10 mv 0.16 0.05 15.3 +14 mv 0.16 0.08 25.6+15 mv

[0018] TABLE 5 Potassium Formate; Fernie Shale % KCOOH % Polymer CST,seconds Zeta Potential 0 0 270 −45 1.10 0 70 −28 mv 1.10 0.02 26.6 −22mv 1.10 0.08 14.4 −21 mv 1.10 0.18 14.6 −18 mv 1.10 0.24 20 −22

[0019] Thus, our invention is seen to include a method of treating ahydrocarbon producing formation to stabilize shale and clay thereincomprising contacting the hydrocarbon producing formation with aformation treatment fluid comprising 1% to 10% by weight of potassiumsalt, determining the Zeta potential of the well treatment fluid, andadjusting the potassium formate content of the well treatment fluid tomaintain a Zeta potential therein at an absolute value greater than 15.

[0020] Further, our invention includes a method of treating ahydrocarbon producing formation to stabilize shale and clay thereincomprising contacting the hydrocarbon producing formation with anaqueous formation treatment fluid comprising 1% to 10% by weight ofpotassium formate, 0.01% to 1.2% of a guar derivative, and up to 50% byvolume calcium carbonate, in) the substantial absence of a hydrophilicclay drilling fluid additive, in particular where the drilling fluid isrecirculated and the percentage of potassium formate is maintainedduring the recirculation by monitoring Zeta potential in the drillingfluid and adding potassium formate thereto to maintain the Zetapotential at an absolute value greater than 15. Our invention furtherincludes a method of drilling a wellbore in an earth formation whilestabilizing shale and clay therein comprising (a) drilling the wellborein the formation with an aqueous drilling fluid comprising from 1% to10% by weight potassium formate and 0.01% to 1.2% of apolygalactomannan, (b) collecting at least one sample slurry of shale orclay particulates obtained from drilling in the earth formation, (c)determining the Zeta potential of the sample slurry in the drillingfluid, and (d) adding or refraining from adding potassium formate to thedrilling fluid to maintain the potassium formate to maintain the Zetapotential within a desired range; in particular where wherein thedesired Zeta potential range has an absolute value greater than 15 andthe drilling fluid is recirculated, followed by at least one iterationof the method of steps (a), (b), (c) and (d) wherein the desired Zetapotential has an absolute value greater than 15.

1. Method of treating a hydrocarbon producing formation to stabilizeshale and clay therein comprising contacting said hydrocarbon producingformation with a formation treatment fluid comprising 1% to 10% byweight of potassium salt, determining the Zeta potential of said welltreatment fluid, and adjusting the potassium formate content of saidwell treatment fluid to maintain a Zeta potential therein at an absolutevalue greater than
 15. 2. Method of claim 1 wherein said formationtreatment fluid includes a viscosifying amount of a polygalactomannan.3. Method of claim 2 wherein said polygalactomannan is a guar.
 4. Methodof claim 4 wherein said guar is carboxymethylhydroxypropyl guar. 5.Method of claim 1 wherein said potassium salt is potassium formate. 6.Method of claim 5 wherein said potassium formate is present in aconcentration of from 2% by weight to 6% by weight of said formationtreatment fluid.
 7. Method of treating a hydrocarbon producing formationto stabilize shale and clay therein comprising contacting saidhydrocarbon producing formation with an aqueous formation treatmentfluid comprising 1% to 10% by weight of potassium formate, 0.01% to 1.2%of guar or a guar derivative, and up to 50% by volume calcium carbonate,in the substantial absence of a hydrophilic clay drilling fluidadditive.
 8. Method of claim 7 wherein said formation treatment fluid isa drilling fluid.
 9. Method of claim 8 wherein said drilling fluid isrecirculated and said percentage of potassium formate is maintainedduring said recirculation by monitoring Zeta potential in said drillingfluid and adding potassium formate thereto to maintain said Zetapotential at an absolute value greater than
 15. 10. Method of claim 7wherein said guar derivative is carboxymethylhydroxypropyl guar. 11.Method of claim 7 wherein said potassium formate is present in aconcentration of 2% to 6% by weight of said formation treatment fluid.12. Method of drilling a wellbore in an earth formation whilestabilizing shale and clay therein comprising (a) drilling said wellborein said formation with an aqueous drilling fluid comprising from 1% to10% by weight potassium formate and 0.01% to 1.2% of apolygalactomannan, (b) collecting at least one sample slurry of shale orclay particulates obtained from drilling in said earth formation, (c)determining the Zeta potential of said sample slurry in said drillingfluid, and (d) adding or refraining from adding potassium formate tosaid drilling fluid to maintain said potassium formate to maintain theZeta potential within a desired range.
 13. Method of claim 12 whereinsaid drilling fluid consists essentially of said potassium formate andsaid polygalactomannan.
 14. Method of claim 12 wherein said guarderivative is carboxymethylhydroxypropyl guar.
 15. Method of claim 14wherein said drilling fluid is substantially free of hydrophilic clayadditive.
 16. Method of claim 14 wherein said potassium formate ismaintained at a 2% to 6% by weight of said drilling fluid.
 17. Method ofclaim 12 wherein said desired Zeta potential range has an absolute valuegreater than 15 and said drilling fluid is recirculated, followed by atleast one iteration of the method of claim 15 wherein said desired Zetapotential has an absolute value greater than
 15. 18. Method of claim 17wherein potassium formate is added to said recirculated drilling fluidat least once.
 19. Method of claim 18 wherein said potassium formateconcentration is maintained in said drilling fluid at a concentration of2% to 6% by weight.
 20. Method of claim 15 wherein said drilling fluidincludes a densifying amount of calcium carbonate.